The background is sealed on the sides. There's 4 grated inlets I made that allow water to flow behind it. Two on the top and 2 hidden near the bottom. The filter intake is actually behind the BG and I'll be able to sitr up behind there to get anything stuck and built up. That's my hopes at least. I guess if I did a proper blog on creating this I would have documented these details... Good points though.
As for the BG taking up a lot of room, it's actually only 5" at the thickest, and 3-4" most places. I chose the thinnest rock one I could get as to give the FRT as much room as possible.
I think next I'm going to get a school or two of smaller fish. Like red striped torpedo barbs and tiger barbs.